Method of superheat control



`June 2, 1953 w. H. ARMAcos-r METHOD OF SUPERHEAT CONTROL Filed Aug. 9.1945 M/M BUR h. ARMA csr 4 INVENTOR.

BY ATT R//Er Patented June 2, 1953 2,640,468 METHOD OF SUPERHEAT CONTROLWilbur H. Armaoost, Scarsdale, N. Y., assignor to CombustionEngineering- Superheater, Inc., a

corporation of Delaware Application August 9, 1945, Serial No. '609,956

2 Claims. 1

The present invention relates to superheaters and particularly toimproved methods of controlling the iinal temperature of superheatedsteam in generators of high capacity.

The single figure in the drawingis a schematic view of a power plantincluding a steam generating boiler in which the temperature ofsuperheated steam is controlled in accordance with the `presentinvention by effecting the major control through burner adjustment toeiect the major regulation by varying the temperature of the products ofcombustion passing over the superheater with the nal regulation beingattained. through a desuperheating action.

The use of tiltable burners alone for the control of steam temperaturehas not been entirely satisfactory. The principle of the tiltable burneris to regulate the temperature of hot gases over the superheatersurface, and thereby control the heat which is transferred from the gasto the steam so as to obtain the steamv temperature desired.

There is one Outstanding disadvantage in the use of tiltable burnerswhich cannot be corrected by design, and that is the sluggishness in theresponse. quate response of the control equipment and the burner tiltingmechanism, but is due rather to the inertia in -changing the temperatureof the large mass of metal embodied in the superheater units I0. In thecase of automatic control the It is not so much a question of ade-Ufor'desuperheating is not of good quality, asmall thermocouple l2 whichis laffectednby the steam temperature leaving the header I4 calls for achange in the setting of the burners 34. On some installations, it takesless than a minute to change the angle of burner tilt, but a period offifteen minutes or more is required to effect a change in steamtemperature because the residual heat in the large mass of thesuperheater keeps raising the temperature above the desired point untila suiicient volume of steam has flowed through to carry ofl' theresidual heat. A reduction in load may be followed by lowering thetemperature of the gases through tilting the burners 34 but even thelower gas temperature tends to keep the steam temperature up and evencause it to rise due to the action of the residual heat of thesuperheater metal on a smaller steam volume. This phenomenon is inherentin the design of tiltable burner control of steam temperature, and isdue to the large mass of the superheater Il). The mass of thesuperheater cannot be reduced and the present trend in design is toincrease it. By the time burner tilting effects the desired change insteam temperature, the

superheater outlet 'of the desired temperature.

need for a change if due to load variations, etc.,

often has passed.

Tiltable burners do have the advantage of effecting relatively largechanges in steam temperature at an economical cost. The inventiontherefore contemplates retaining the advantages 1 of a tilting burnertype of steam temperature control and the use of additional controls toOffset the disadvantage of sluggishness to effect a major part of theregulation in steam temperature, and achieve the final regulation byother controls.

The quickest acting control is a spray desuperheater 20 located beyondthe superheater outlet I4. range of control-Of about 15 degrees to 25degrees F. at maximum load on the boiler. used for desuperheating wouldbe drawn from the feed Water heater or feed water itself, if ofsufficient purity. A valve 24 in the feed water line 22 is operable inresponse to the fluctuations in steam temperature at or near the turbine26 as reflected bya thermostat 28. By proper manipulation the steamtemperature at the turbine or engine can be maintained within 2 degreesF. By limiting the range of auxiliary desuperheater control to the nall5 degrees to 25 degrees F. of regulation the percentage of Water usedfor this purpose is kept to a minimum.

For .installations in which the water available non-contactdesuperheater may be used which would be lplaced in one of the boilerdrums. It is possible to design such a desuperheater which can beinstalled assembled through a standardv manhole opening, and which willhave maximum range of control of l5 degrees to 25 degrees FK. With sucha design the heat removed from lthe superheated steam would betransmitted through the tubes of the desuperheater into the boilerwater. The reaction in response to a change in steam temperature wouldbe many times faster than the reaction obtained solely with tiltingburner control in that a considerably less mass of metal would beaffected. The response would not be quite as fast as in the case of thespray type of desuperheater.

The small non-contact type of desuperheater would be connected so as towithdraw part of the superheated steam from the outlet header I4. Inthis respect the connection can be made at the blank end of the outletheader, thereby requiring a slightly smaller outlet header. The part ofsteam withdrawn would be passed through the desuperheater and itstemperature reduced to a Such a spray would be designed to give a Thewater point so that when returned and mixed with the main steam ow theresultant steam temperature will be that desired.

In boilers equipped with tilting burners regulation is effected bytilting the furnace burners vertically to vary the vertical position A,B, or D of the combustion zone with respect to water Walls or byadjusting burners'horizontally to change*l the size andlocation ofthecombustion zone by altering the size of a circle toward which the flamesare directed tangentially and thus in' either case to vary the degreeofcocling oiv the:

gases by the furnace walls prior to reaching the superheater. Suchcontroli arrangements are more fully disclosed in Kreisinger et al'.4Patent' 2,363,785 issued November 28, 1944, and Kruger Patent 2,243,909,issued June 3,4 1941/, respectively; With such installations the majoramount of control may be effected by adjustment of the burners 34 andthe final 15 degrees-,to 25 degrees by passing. parti of the steamthrough: the desuper-v heater 3i?.

What I claim is:

l. The method of: maintaining superheat'ed' steam temperature inasteam'generator in-vvvlfii'ch` the major portion ofthey steam isproduced' in` a vertical furnace'lined with steam generating elementsexposed to radiant neatV from burning fuel andi Which generators havesuperheat'ersl of relatively large heat storage capacity, due to themetallic mass-thereof; suflicient to cafuse'- a substantial time l'ag'inthe change of'steam4 temperature when the-volume and temperature of'heating' gases passing over the superheater decrease with the f-uel'?burningv rate upon a fall insteam demand, Which comprises: introducingfuel and' air into the furnace in'- such directions so as to create aturbulent gas mass in a zone remote from the furnace outlet; burningsaid fuel at a rate in accordance With steam demand and absorbingtheradia-nt heat therefrom `in the steam generating elements to producesteam to be superheated; passing the steam so generated through thesuperheater to increase its temperature; controllably altering theangle` of` introduction of fuel and air' to the furnace to lower" thezone-of' combustion with respect to the steam generating elements thatabsorb radiant'heat so as to increase said absorption and reduce thetemperature of gasesv passing over the superheaterto compensate for onlythe` major part offincreases'above a predetermined value ofisteamtemperature leavingthe superheater; and simultaneously subjecting allorv part ofi the super'- heated: steam toa desuperheating action so asto promptly offset the overheating of all of' the steam, during saidlag; due to said heat storage in the superheater metal to effect minoradjustments of steam temperature during'a change in load therebymaintaining a substantially constant nal steam temperature.

2. The method of maintaining final temperature of steam in a superheaterreceiving its heat mainly by convection from gases leaving a furnaceprovided with water cooled tubes in which the major portion of the steamisiproduced by radiantiabsorption of heat from fuel! burned in thefurnace and which generators have superheaters of relatively large heatstorage capacity suiiicient to cause a substantial time lag, due tothe.metallicmass'thereof, in the change of steam temperature when thevolume and temperature `of the heating gases'passing over said super-151 heater changes with' increase or decrease of the fuelburningrate'upon change in steam demand, which comprisestintroducingfuel and air into the furnace in such directions as to create aturbulent' gas mass in av zone remote from the furnace outlet; burningsaid fuel at a rate in accordance.- with steam demand' and absorbingradianty hea-t1therefromy in the steam generatingelements to pro-ducesteam to be superheated': passing steam so generatedv throughy thesuperheater. to' increase its temperature; controllabl'y altering the.angle of introductiony of fuel andair.' into the furnace *so as: to`rshift the Zone ofl combustion. toward or away from the furnaceI outletso as to decreaseor increase, respectively;

the absorption of radiant heat in said steam generating elements and?thereby increaseJ and: reduce, respectively, the temperature ofheat'-4ing gases passing' over thesuperheater and thus compensate for only themajor part of variations from a predetermined value of the steamtemperature leaving the superheater; and sub jecting all or part of thesuperheated steam to' a desuperheating action for promptly offsetting'the overheatingv of allofI the steam, during said lag. due to saidheatstorage in the superheaterv metal so as to effect minor adjustmentsof steaml temperature occurring as a result of increasing and'decreasing the temperature of the gases passing over the superheaterthereby maintaining a substantially constant' final steam tem-1perature.

WILBUR I-I. ARMACOSTL References Citedin the file ofthis. patent UNITED"STATES PATENTS- Number Name Date 2,363,875 Kreisinger et al. Nov.28,419.44

FOREIGN PATENTS Number Country Date 409275' Germany Feb. 3, 1925 43?;534GermanyA Nov. 24,1926 482.901 Great Britain Apr. 7, 1938

